CN110596917A - Terahertz wave light-operated modulator and preparation method thereof - Google Patents
Terahertz wave light-operated modulator and preparation method thereof Download PDFInfo
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Physics & Mathematics (AREA)
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- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
A terahertz wave light-operated modulator based on a passivation process to grow a passivation film and a preparation method thereof are disclosed, wherein passivation layers are deposited on a terahertz wave incident surface and a terahertz wave emergent surface of an intrinsic semiconductor material by utilizing an atomic layer deposition system, a plasma enhanced chemical vapor deposition method or a low-pressure chemical vapor deposition method, and the passivation layers are aluminum oxide films, silicon nitride or silicon oxide. The surface defects of the intrinsic semiconductor material are improved by using a passivation process, so that higher carrier concentration is obtained, the requirement and cost of a terahertz wave correlation system on illumination can be reduced, and the system is more integrated and is convenient for operation of a user. In addition, the passivation layer can isolate the contact of the semiconductor and air, prevent oxidation and pollution, enhance the stability of the terahertz wave light-operated modulator and prolong the service life of the modulator.
Description
Technical Field
The invention relates to the technical field of terahertz wave sensing and imaging, in particular to a terahertz wave regulating and controlling device.
Background
Terahertz wave refers to (frequency)Rate 1011Hz-1013Hz or wavelength 30 μm-3mm) between the microwave band and the optical band. It is in a particular position in the transition from electronics to photonics in the electromagnetic spectrum and therefore has unique properties. For example, many important biological molecules (e.g., proteins, DNA) and biological cells are characterized by low frequency vibrations (e.g., collective vibrations of the backbone of the molecule, rotation, and weak forces between molecules) in the terahertz spectrum (spectral fingerprinting). Based on terahertz spectrum analysis, relevant information such as spatial conformation, reaction kinetics, hydration, biological function and the like of biomolecules can be analyzed. In addition, terahertz wave can penetrate through various nonpolar materials (paper, plastic, ceramic and the like), and hidden target imaging is realized. Particularly, compared with the widely applied X-ray, the terahertz wave has lower photon energy (0.41-41meV), so that the terahertz wave has no damage to biological molecules and no ionization to biological cells, and can be used as an ideal biomedical nondestructive detection means. The sensing and imaging of terahertz waves are regarded as one of the most important application technologies of terahertz waves, and abundant physical and chemical information of a sample to be detected is obtained by analyzing the interaction between the terahertz waves and the sample to be detected, so that the terahertz waves are generally concerned by scientific research and the industry due to the intuition.
The terahertz wave modulator is an indispensable device for researching terahertz wave sensing and imaging, and the efficient and stable terahertz wave regulating and controlling device is the basis for researching terahertz science and technology. Since the start of the terahertz wave technology is late, an effective terahertz wave modulator device still needs to be developed. The modulation mechanism for regulating and controlling the terahertz waves comprises amplitude modulation, frequency modulation, phase modulation and polarization modulation. At present, the mature regulation and control mode of terahertz waves is amplitude modulation control, the realization means comprises electric control, light control, thermal control and nonlinear control, and the change of certain parameters of a modulator, such as refractive index, absorptivity and other parameters, is controlled through external change, so that the transmissivity or reflectivity of the terahertz waves is controlled.
Among the existing terahertz wave modulator devices, light-operated semiconductor (such as silicon, germanium, gallium arsenide, etc.) modulators are widely used in terahertz wave imaging and terahertz wave communication systems. The light control method is characterized in that pumping light is utilized to irradiate a semiconductor, and when photon energy exceeds the forbidden bandwidth of the semiconductor, carriers are generated, so that the conductivity of the semiconductor is changed, the transmittance of terahertz waves is influenced, and the function of controlling the terahertz waves by the pumping light is realized. The light control method has high control speed and high control accuracy, and is generally accepted by people. In general, the pump light can adjust the terahertz wave by irradiating the pump light onto the semiconductor to generate a temporary region with high reflectivity, and the terahertz wave is simultaneously incident on the region with high reflectivity, so that the terahertz wave is modulated by changing the on-off of the pump light. Shrekhamer et al irradiates intrinsic semiconductor silicon with a 980nm continuous laser at an output of 2W to realize a modulation depth of 67% for terahertz waves (modulation depth ═ terahertz wave transmittance without illumination-terahertz wave transmittance with illumination)/terahertz wave transmittance without illumination); busch et al achieved 94.8% modulation depth by irradiating intrinsic silicon with a 100fs laser; born et al use a 808nm continuous laser to output 2.28W of power to irradiate intrinsic silicon to realize 90% of modulation depth of terahertz waves. However, in order to realize that the modulation device effectively regulates and controls the terahertz waves and obtain higher photo-generated carrier concentration, such modulators often need to be equipped with a high-energy laser for illumination, such as a common amplified femtosecond laser, which substantially increases the cost and complexity of the whole system, is not beneficial to the integration of the system, cannot guarantee the safety in implementation, cannot recognize the operability, and cannot meet the integration requirements of terahertz wave imaging, sensing and communication.
In contrast, in the prior art, the efficiency of the terahertz wave light control modulator can be improved by utilizing the heterojunction effect of the two-dimensional material and the semiconductor, so that the requirement of the light control modulator on illumination is reduced. Weis and the like transplant single-layer graphene on intrinsic silicon, most of carriers excited by silicon flow to the graphene by utilizing the high electron mobility of two-dimensional graphene, and then the carrier concentration is sharply increased, so that the high-efficiency terahertz wave modulation is realized. On the same principle, the illiterate industry and the like transfer single-layer graphene on intrinsic germanium, and a 1550nm laser is used for illumination, so that the 94% modulation depth is realized; in addition, yangtong et al propose transfer of WS2 nanoplates on intrinsic silicon, achieving 56.7% terahertz wave modulation at 800nm continuous laser, 50mW illumination, 94.8% terahertz wave modulation at 470 mW. Even so, because the two-dimensional material is usually not stable enough, great problems will be brought about in the preservation and use of the device, and it is also very difficult to prepare the two-dimensional material on the device, and the cost of manufacture itself is high, which makes the terahertz light control modulator prepared with the two-dimensional material difficult to be moved out of a laboratory to meet practical applications.
Based on the current situation, in the field of terahertz wave sensing and imaging technology, a better technical scheme is obviously needed to solve the technical problems of high cost, high complexity, difficulty in storage and the like of the existing light-operated semiconductor modulator.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a terahertz wave efficient light control modulator based on a passivation process based on the attributes of semiconductor materials. Through the passivation technology, the service life of a current carrier of the semiconductor device is prolonged, the modulation depth of the semiconductor device is greatly improved, and meanwhile, the passivation layer has a protection effect on the device, so that the device is further far away from the influence of the external environment, and the whole semiconductor device has better stability.
Specifically, the application provides a method for preparing a terahertz wave light-operated modulator, which selects an intrinsic semiconductor material and is characterized in that passivation layers are respectively deposited on a terahertz wave incident surface and a terahertz wave emergent surface of the intrinsic semiconductor material; the deposition operation uses one of an atomic layer deposition method, a plasma enhanced chemical vapor deposition method, or a low pressure chemical vapor deposition method; the passivation layer is made of aluminum oxide, silicon nitride or silicon oxide.
In one embodiment, when the deposition operation is completed using an atomic layer deposition system, the deposition operation includes the steps of:
s21, self-cleaning of the atomic layer deposition system;
s22, preheating the atomic layer deposition system, and placing a semiconductor material;
s23, setting system parameters, wherein the system parameters comprise the deposition cycle number;
s24, depositing a passivation layer on the terahertz wave incident surface or the terahertz wave emergent surface of the semiconductor material;
s25, taking out, turning over and repeating the steps S21-S24;
s26, placing the blank into an annealing furnace for rapid annealing;
wherein, in the step S22, before the semiconductor material is placed, a protection operation is further performed on the non-deposition surface of the semiconductor material. The protective operation is preferably performed by adhering a polyimide film to the non-deposition surface. Alternatively, the protecting operation may be performed by placing the non-deposition surface in close proximity to a surface of another semiconductor material.
Further preferably, the passivation layer is subjected to antireflection treatment, and the antireflection treatment includes selecting an optimal thickness of the passivation layer according to an incident angle when the terahertz wave light-operated modulator is used; the optimal thickness is such that the reflectivity of the passivation layer is lowest. Further, the number of deposition cycles in the step S23 is determined according to the optimal thickness, so as to prepare a passivation layer with a proper thickness.
Specifically, when the passivation layer is aluminum oxide, the step S23 includes setting the aluminum source flowing time to be 8S, the nitrogen purging time to be 23S, the water source flowing time to be 8S, and setting the number of deposition cycles to be 1230.
A cleaning process may be further included before step S21 to clean the semiconductor material during transportation; the cleaning process comprises the following steps:
s11, cleaning the semiconductor material by using acetone;
s12, washing with ultrapure water;
s13, etching by using hydrofluoric acid;
s14, taking out the etched semiconductor material, and adding ultrapure water for cleaning.
Preferably, the step S26 is a rapid annealing at 400 ℃ for 5 minutes under a nitrogen atmosphere.
Correspondingly, the application also provides a terahertz wave light-operated modulator prepared by the preparation method.
Compared with the prior art, the invention adopts a brand new means, namely the terahertz wave light-operated modulator is prepared by using a passivation process, so that the surface of the modulator is provided with a passivation layer and can have higher photo-generated carrier concentration, thus realizing the high-efficiency modulation of the terahertz wave light control, reducing the requirements of the terahertz wave relation system on illumination and the cost of the system, being convenient for the system to be more integrated and being more convenient for the user to operate and use. In addition, the passivation layer can also isolate the contact of a semiconductor and air, and prevent oxidation and pollution, so that the stability of the terahertz wave light-operated modulator is enhanced due to the introduction of the passivation process, and the service life of the modulator is prolonged.
The foregoing description is only an overview of the technical solutions of the present application, and in order to make the technical solutions of the present application more clear and clear, and to implement the technical solutions according to the content of the description, the following detailed description is made with reference to the preferred embodiments of the present application and the accompanying drawings.
Drawings
FIG. 1 is a schematic view of the process for preparing an alumina film by the passivation process of the present invention;
FIG. 2 is a schematic view of a single layer antireflective film;
FIG. 3 is a graph showing the variation of reflectivity and minimum reflective film thickness with incident angle;
FIG. 4 is a schematic diagram of the selection of the optimal thickness of the film at a fixed incident angle;
FIG. 5 is a schematic diagram of an enhanced imaging experiment;
FIG. 6 is a flow chart of an imaging implementation method.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be described in detail and completely with reference to the following specific embodiments of the present application and the accompanying drawings. It should be apparent that the described embodiments are only some of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The basic working principle of the terahertz wave light-operated modulator is that pumping light is utilized to irradiate a semiconductor, when photon energy exceeds the forbidden bandwidth of the semiconductor, the semiconductor can generate photon-generated carriers, and the concentration of the carriers can change the conductivity of the semiconductor. Terahertz waves are electromagnetic waves to which semiconductor materials such as intrinsic silicon (or germanium) are transparent. However, if the concentration of photogenerated carriers increases, the conductivity of the semiconductor increases, thereby affecting the transmittance of the terahertz wave, which decreases as the concentration of carriers increases. According to the formula
Wherein n is the refractive index 3.418, the transmittance T and the conductivityIn inverse ratio, Z0377 Ω, d semiconductor thickness, f frequency, m relative mass, ε0Is the vacuum dielectric constant and e is the charge amount. Carrier concentration N proportional to conductivityTherefore, the larger the conductivity is, the larger the carrier concentration is, and the lower the transmittance of the terahertz wave is. The photogenerated carrier concentration also depends on temperature, light, semiconductor material, etc. Under the conditions that the device is not changed and the environment temperature is not changed, the carrier concentration can be directly changed by changing the illumination intensity according to a formula
Where a is the illumination area size, R is the reflectivity, h υ is the photon energy, d is the device thickness, and τ is the carrier lifetime (the average time from generation to recombination of photogenerated carriers). The carrier concentration N is proportional to the illumination intensity I, which is also the reason why the conventional photo-modulator uses high-power laser illumination to achieve high modulation depth. However, in addition to the illumination conditions, certain parameters of the semiconductor material itself may also determine the carrier concentration, such as carrier lifetime τ. The carrier concentration N and the lifetime τ are also in a proportional relationship. Carrier lifetimes include semiconductor body lifetimes, surface lifetimes and starvation lifetimes,
since low resistance attenuates terahertz waves in the terahertz wave band, a high-resistance intrinsic semiconductor is often used. For intrinsic semiconductor materials, however, since bulk defects are small, the lifetime of the charge carriers is very large, and the crystal lattice is relatively stable, and the lifetime of starvation is not considered, only the surface lifetime in formula (3) needs to be considered when considering the lifetime of the charge carriers in formula (2). In the case where the carrier lifetime of the modulator is mainly determined by the surface lifetime, the most significant factor affecting the carrier lifetime (i.e., affecting the surface lifetime) is also the surface defect, and the surface defect generally includes surface-attached impurities, a sacrificial oxide layer on the surface, and the like. Due to the presence of surface defects, defect levels are introduced, and the generated carriers are heavily recombined by the defects, resulting in a reduction in carrier lifetime. Therefore, if the surface defects can be improved, it will be possible to maintain the carrier lifetime at a large value, so that a higher carrier concentration can be obtained, which would be very advantageous for the terahertz wave modulator.
Passivation processes were first used on metals, with the activated metal being protected from corrosion by metal oxides. Subsequently, the process is also used for the preparation of a solar cell processing anti-conductive insulating layer and the packaging in the semiconductor field. In semiconductor devices such as silicon chips and the like, the passivation process can improve surface defects and protect the semiconductor from being oxidized by the outside, and the characteristics can help to improve the performance of the terahertz light-operated modulator. In the passivation process, an Atomic Layer Deposition (ALD) system, a Plasma Enhanced Chemical Vapor Deposition (PECVD) method or a Low Pressure Chemical Vapor Deposition (LPCVD) method may be used to deposit passivation on the semiconductor materialLayers, e.g. depositing aluminium oxide film (Al)2O3) Silicon nitride or silicon oxide. The deposited passivation layer has the characteristics of dense film and good uniformity, so that the passivation layer can be widely used for semiconductor materials. Based on the above characteristics of the passivation process, the present invention provides a terahertz wave light control modulator based on a passivation process to grow a passivation film, wherein a passivation layer, such as an aluminum oxide film (Al) is deposited on an intrinsic semiconductor material by using an atomic layer deposition system (ALD), a Plasma Enhanced Chemical Vapor Deposition (PECVD) or a Low Pressure Chemical Vapor Deposition (LPCVD) method2O3) And silicon nitride or silicon oxide, thereby improving the surface defects of the intrinsic semiconductor material, obtaining higher carrier concentration and reducing the requirement of the terahertz wave modulator on illumination.
Example a Process for preparing a Modulator deposited alumina film
In this example use<100>The n-type double-polished intrinsic silicon wafer with the crystal orientation has the resistivity of 10000 omega cm and the thickness of 100 mu m. A thermal ALD system is employed with trimethylaluminum and water as reaction sources, argon as a carrier gas, and nitrogen as a purge gas. Sample deposition was performed at 250 ℃. The reaction principle of passivation is as follows: 2Al (CH)3)3+3H2O→Al2O3+6CH4. Then, the fabricated device was annealed at 400 ℃ for 5 minutes in a nitrogen atmosphere using a rapid annealing furnace. The specific manufacturing process flow of the modulator is shown in the attached figure 1 of the specification, and mainly comprises a silicon wafer cleaning flow and an alumina film deposition flow (silicon wafer passivation).
Pollutants are always introduced into the silicon wafer in the transportation and storage processes, and the silicon wafer needs to be cleaned in order not to influence the overall performance of a device. Firstly, adding a proper amount of acetone solution to carry out ultrasonic cleaning in step S11, wherein the step is to remove organic matters on the surface; then step S12 ultrasonic cleaning with pure water to remove the redundant acetone solution; step S13 is carried out by using hydrofluoric acid for cleaning, and an oxide layer on the surface of the silicon chip is eliminated, so that a silicon-hydrogen bond is formed on the surface of the silicon chip; and finally, step S14, ultrasonic cleaning with pure water, and removing redundant hydrofluoric acid waste liquid. Preferably, the ultrasonic cleaning water bath in steps S11, S12 and S14 is for 5 minutes. The concentration of hydrofluoric acid in step S13 was 40%, and etching was performed for 10 minutes.
And after the silicon wafer cleaning process is completed, the cleaned silicon wafer is placed into ALD equipment for deposition, and the alumina film deposition process is completed. Because the invention aims to improve the surface defects of the silicon wafer, for the silicon wafer for manufacturing a modulator generally, both surfaces of the silicon wafer need to be processed, otherwise, the surface defects of the other surface can influence the concentration of carriers if only one surface is processed. However, since ALD can process only one side at a time, it is necessary to prevent contamination of the non-deposition side during deposition on one side. In this example, the non-deposition side was selected to be protected by a high temperature polyimide film. Before the silicon wafer is placed into the device, a polyimide film is used for covering and protecting one surface, then the silicon wafer is placed into the ALD device for passivation deposition of the other surface, after the deposition of the surface is completed, the silicon wafer is taken out, the polyimide film is uncovered, the surface on which the aluminum oxide is just deposited is coated with polyimide for protection, the silicon wafer is placed into the ALD device again, and the other surface which is not deposited is deposited. Alternatively, another silicon wafer may be used to perform the above function of protecting the non-deposition surface. Specifically, the silicon wafer is placed on the other silicon wafer, so that the contact surfaces of the two silicon wafers are protected, the silicon wafer on which the passivation layer is deposited is turned over and placed on the other silicon wafer again after the treatment of one surface is finished, and the deposited passivation layer is protected in the next deposition process.
The specific alumina film deposition process comprises the steps of self-cleaning of the ALD equipment in the step S21, turning on a mechanical pump, vacuumizing, turning on a nitrogen gas valve, and setting the cleaning time to be 120S; after cleaning, placing a silicon wafer with one surface adhered with a polyimide film in step S22, enabling the surface adhered with the film to face the bottom of the reaction furnace, setting the substrate temperature of the reaction furnace to be 250 ℃ and the aluminum source temperature to be 90 ℃, starting a water circulation protection machine, and waiting for a period of time to observe the temperature conditions of all parts to finish preheating operation; next, in step S23, an aluminum source flowing time 8S, a nitrogen purging time 23S, a water source flowing time 8S, and a nitrogen purging time 23S are set; setting the cycle number 1230 times; after the parameters are set, step S24 opens the mechanical valves for the aluminum source and the water source, sets the flow rates of argon and nitrogen, and starts the deposition. And after the deposition of one side is finished, performing step S25 to open the cavity, taking out the silicon wafer, tearing off the polyimide film, turning over the silicon wafer, and repeating the steps S21-S24 to finish the deposition of the other side of the silicon wafer. And finally, in the step S26, after the two sides are deposited, the silicon wafer is taken out and put into an annealing furnace, and the rapid annealing is carried out for 5 minutes under the atmosphere of nitrogen at 400 ℃.
In order to efficiently utilize the energy of illumination photons, the deposited aluminum oxide film is further used as an anti-reflection film to reduce the reflection effect on illumination light, thereby further increasing the carrier concentration. The design principle of the single-layer anti-reflection film is shown in FIG. 2, the wavelength of the illumination light source suitable for the designed film is lambda, and the refractive indexes corresponding to air, aluminum oxide and silicon wafer are n respectively0、n1、n2According to Snell's theorem, the reflection coefficient r of the interface can be calculated1、r2The phase difference of the light emitted from the two surfaces isTherefore, a formula of the change of the reflectivity R along with the thickness h of the film can be calculated.
Theoretically, photon energy exceeding the semiconductor forbidden band width can excite photon-generated carriers. In a silicon wafer, a light source with the forbidden band width of 1.12eV and the wavelength of less than 1100nm can excite carriers. In the modulation process of terahertz waves, an infrared light source 808nm is generally selected as an illumination light source to excite carriers. In this illumination case, the refractive indices of air, alumina, and silicon wafer are 1, 1.76, and 3.68, respectively. The variation trend of the reflectivity under different incident angles is calculated by using Matlab simulation and is shown in FIG. 3, wherein the X axis is the incident angle, and the Y axis is the reflectivity and the optimal film thickness. The lower left curve shows that the reflectivity gradually increases with increasing incidence angle, and at this time the optimal film thickness (the upper left curve in fig. 3) is obtained at different incidence angles, and the optimal film thickness gradually increases from 125nm with increasing incidence angle. When the incident angle exceeds 80 degrees, the influence of the film is almost negligible, and the optimal thickness of the film is not mentioned. In FIG. 3, when the incident angle is less than 60 degrees, the reflectivity is less than about 5%, and the corresponding film thickness is less than about 134 nm.
If the incident angle is fixed, for example, 40 degrees, the film thickness at the lowest reflectance point is determined to be 123nm as shown in FIG. 4, and the reflectance at this time is only about 1%. Since ALD is deposited with a thickness of 0.1nm at a time, the number of deposition cycles of step S23 is set to 1230 in the present embodiment in the deposition flow, thereby obtaining an alumina passivation film with a film thickness of 123 nm. When the incident light of the light-operated modulator prepared in the way is 808nm and the incident angle is 40 degrees, the thickness of Al2O3The reflectivity of the film is lower than 1 percent, so that the antireflection effect is achieved. Since the silicon wafer is illuminated by light with 808nm wavelength generally has 30% reflection loss, if the anti-reflection design is added according to the present embodiment, at least 30% of the energy is saved, so that, for example, laser with 3W output power originally required can be replaced by LED with 2W output power according to the solution of the present embodiment, which further reduces the cost of the system.
Second embodiment terahertz wave enhanced imaging based on modulation
Description figure 5 is a schematic diagram of an embodiment of implementing terahertz single-pixel enhanced imaging by using a passivated terahertz wave light-operated modulator. An imaging target 10 is attached to the back of a terahertz wave light-operated modulator 1 as shown in fig. 5, 800nm femtosecond laser is divided into two beams of light through a beam splitter 2, one beam of light enters a transmitting end 3 to generate terahertz waves, and the other beam of light irradiates a receiving end 5 through a delay line 4. The generated terahertz light is collimated by the discrete parabolic mirror 61 and irradiates the terahertz wave light-operated modulator 1, the transmitted terahertz wave is focused on the receiving end 5 by the discrete parabolic mirror 62, and the terahertz wave is coherent with the femtosecond light to obtain a transmitted terahertz light field. The terahertz time-domain signal transmitted through the terahertz wave light-operated modulator 1 can be obtained by scanning the delay line 4.
Continuous light is collimated and then irradiates on the terahertz wave light-operated modulator 1, terahertz waves and continuous laser are irradiated in the same area of the modulator, and the intensity of the terahertz wave transmittance is adjusted and controlled by controlling the on-off of the continuous laser. The 808nm laser is modulated by a Digital micromirror array (DMD) 7, so that a spatially distributed mask is formed on the surface of the terahertz wave light-operated modulator 1, and because the illumination area can block the terahertz wave, the coded mask on the DMD indirectly modulates the terahertz wave signal. The target field intensity of the terahertz wave is demodulated through a projection mask and a measured value by utilizing an advanced single-pixel imaging algorithm, such as compressed sensing, computational imaging and the like. According to the basic imaging formula Y ═ Φ X, where the matrix of the object to be imaged is expressed as X, the measured values Y, Φ are the measurement matrices (corresponding masks), and Φ is set as an orthogonal matrix with noise-resistant capability for demodulation of X, so that the object image X ═ Φ' Y. The measurement matrix satisfying this condition includes a hadamard matrix, a bernoulli matrix, a fourier matrix, and the like. The imaging method is shown in figure 6 in the specification, and specifically comprises the following steps. Step S31, placing a target to be imaged on the back of the terahertz wave light-operated modulator, expressing the target to be imaged as X, and placing the X and the light-operated modulator into a light path; step S32, finding the maximum signal position of the terahertz wave transmitting the sample by using a delay line; step S33, making N2×N2The terahertz wave intensity modulation method comprises the following steps of (1) a Hadamard matrix (or a Bernoulli matrix and the like), wherein an exemplary N is 64, taking out each line, shaping to obtain an N multiplied by N mask pattern, projecting the pattern onto the terahertz wave light-operated modulator, and reading out and modulating terahertz wave intensity Y by using a detector; step S34 demodulates the formula X ═ Φ' Y to obtain a terahertz wave image of the target.
Therefore, compared with single-pixel imaging in the prior art, the imaging system based on the passivated process light control modulator has the advantages that the contrast of an imaged image can be enhanced under the low illumination requirement, and a clearer image can be obtained under the illumination with the same power.
In conclusion, the invention can improve the service life of the silicon chip carrier and improve the concentration of the photon-generated carrier based on the passivation process, and the process is used for manufacturing the terahertz wave light-operated modulator to realize the high-efficiency modulation of the terahertz wave light control. Therefore, the requirements and cost of the terahertz wave correlation system on illumination are reduced, and the system is convenient to integrate and operate by users. In addition, the passivation layer can isolate the contact of a semiconductor and air, prevent oxidation and pollution, enhance the stability of the terahertz wave light-operated modulator, prolong the service life of the modulator and provide a prerequisite for being taken out of a laboratory for wide application.
The above description is only for illustrating the embodiment of the terahertz wave light control modulator of the present invention, and since it is easy for those skilled in the same technical field to make several modifications and changes based on the above description, the present specification does not intend to limit the modulator of the present invention to the specific structural scope shown and described, and therefore all modifications and equivalents that may be utilized belong to the claims of the present invention.
Claims (10)
1. A method for preparing a terahertz wave light-operated modulator selects an intrinsic semiconductor material, and is characterized by comprising the following steps of:
respectively depositing a passivation layer on a terahertz wave incident surface and a terahertz wave emergent surface of the intrinsic semiconductor material;
the deposition operation uses one of an atomic layer deposition method, a plasma enhanced chemical vapor deposition method, or a low pressure chemical vapor deposition method;
the passivation layer is made of aluminum oxide, silicon nitride or silicon oxide.
2. The method of claim 1, wherein the depositing is accomplished using an atomic layer deposition system, the depositing comprising:
s21, self-cleaning of the atomic layer deposition system;
s22, preheating the atomic layer deposition system, and placing a semiconductor material;
s23, setting system parameters, wherein the system parameters comprise the deposition cycle number;
s24, depositing a passivation layer on the terahertz wave incident surface or the terahertz wave emergent surface of the semiconductor material;
s25, taking out, turning over and repeating the steps S21-S24;
s26, placing the blank into an annealing furnace for rapid annealing;
wherein, in the step S22, before the semiconductor material is placed, a protection operation is further performed on the non-deposition surface of the semiconductor material.
3. The method of claim 2, wherein the protecting operation is adhering a non-deposition surface with a polyimide film.
4. The method of claim 2, wherein the protecting is accomplished by placing the non-deposition surface in close proximity to a surface of another semiconductor material.
5. The method according to claim 2, wherein the passivation layer is subjected to an antireflection treatment, the antireflection treatment including selecting an optimum thickness of the passivation layer according to an incident angle when the terahertz wave light control modulator is used; the optimal thickness is such that the reflectivity of the passivation layer is lowest.
6. The method of claim 5, wherein the number of deposition cycles in step S23 is determined according to the optimal thickness.
7. The method of claim 6, wherein the step S23 comprises setting the flow time of the aluminum source to 8S, the purge time of the nitrogen gas to 23S, the flow time of the water source to 8S, and setting the number of deposition cycles to 1230.
8. The method of claim 2, wherein: a cleaning process is also included before step S21; the cleaning process comprises the following steps:
s11, cleaning the semiconductor material by using acetone;
s12, washing with ultrapure water;
s13, etching by using hydrofluoric acid;
s14, taking out the etched semiconductor material, and adding ultrapure water for cleaning.
9. The method according to claim 2, wherein the step S26 is a rapid annealing at 400 ℃ for 5 minutes under a nitrogen atmosphere.
10. A terahertz wave light control modulator prepared by using the method of any one of claims 1 to 9.
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